Method of stabilizing halogenated aliphatic and in particular ethylenic hydrocarbons



METHOD OF STABILIZING HALOGENATED ALI- PHATIC AND IN PARTICULAR ETHYLENIC HYDROCARBONS Georges Wetrolf, Le Thillay, and Claude Kaziz, La

Courneuve, France, assignors to Pechiney, Compagnie de Produits Chimiques et Electrometallurgiques, Paris, France, a corporation of France No Drawing. Filed Aug. 1, 1958, Ser. No. 752,395

Claims priority, a plication France Aug. 8, 1957 15 Claims. (Cl. 260652.5)

This invention relates to a new method for the stabilization of halogenated aliphatic and in particular ethylenic hydrocarbons which have one or two carbon atoms per molecule, and in particular to hydrocarbons of this kind in which from two to four hydrogen atoms per molecule are substituted by chlorine atoms.

The invention also relates to industrially useful ethylenic hydrocarbons having up to two carbon atoms and from two to four chlorine atoms per molecule and which are stable due to changes secured by means of the method according to the invention.

The problem of stabilizing halogenated aliphatic and in particular ethylenic hydrocarbons of the type described above, among which there are in particular trichloroethylene, perchloroethylene and tetrachloroethylene is very dilficult to solve in a satisfactory manner which permits to obtain a sufficiently high degree of stabilization with commercially feasible means.

It is an object of our invention to provide a method for stabilizing halogenated hydrocarbons of the type described by means of a stabilizing agent which is both easily available commercially and does not cause the formation of undesirable byproducts in the hydrocarbons treated therewith.

-It is another object of our invention to provide a hydrocarbon of the type described which is stable and free from undesirable, poisonous or malodorous byproducts.

It has not been possible to solve the above-mentioned problem satisfactorily in the past. All known processes either do not permit to obtain a sufficiently high degree of stabilization or the substances required as stabilizing agents are difficult to produce and therefore so expensive that the costs of using them on a large industrial scale would be prohibitive.

As a third drawback of the processes known in the art, the substances introduced as stabilizers are decomposed during the stabilizing reactions which take place between the same and the halogenated aliphatic and in particular ethylenic hydrocarbons of the kind described, and lead to the formation of byproducts, which are of a poisonous or otherwise disagreeable nature, and the necessary removal of which makes the known methods complicated and unduly expensivev Among the substances known in the art as stabilizers for halogenated low molecular aliphatic and in particular ethylenic hydrocarbons having from two to four halogen atoms per molecule there have been proposed also frequently compounds of divalent sulfur, which are derivatives of H 8. Among these there have been suggested organic derivatives such as mercaptan thiazoline, thiophene (Patents 2,517,893 and 2,621,215 respectively), and other inorganic or organic compounds containing divalent sulfur as well as at least one carbon atom per molecule among which there are thiourea and carbamides (Patent 2,043,258) and thiocyanates (Patent 2,108,390), and finally dithiocarbamate salts and derivatives thereof (Patent 2,532,660), the latter salts, however, only for stabilizing mixtures of hydrocarbons of the above described type with halogenated aromatic hydrocarbons.

All of these substances suffer from the above stated drawbacks, Other substances among which there are elementary sulfur or divalent sulfur in the form of thiosulfate salts containing at least one divalent sulfur atom per molecule have not been found satisfactory in the treatment of halogenated low molecular weight aliphatic and in particular ethylenic hydrocarbons of the type described and have been used only for high molecular weight chlorinated parafiin derivatives, in particular those having twelve and more carbon atoms per molecule and obtained from parafiin wax and the like, while it had been found that the divalent sulfur compounds such as mercaptan were completely ineffective as stabilizers for these higher chlorinated parafiins.

In order to find a satisfactory stabilizing agent for the ethylenic hydrocarbons described, it must be taken into account that the instability of these compounds is different in nature from that of the other chlorinated organic compounds, both parafiinic or aromatic that have been mentioned above. We assume that the instability of the halogenated aliphatic and in particular ethylenic hydrocarbons with which the present invention is concerned, is due to the presence in the hydrocarbon molecule of excessive chlorine atoms bonded by association rather than by normal homopolar bonds to the ethylenic double bond in the hydrocarbon molecule, or, also by association or covalency bonds, to the short molecules of more highly chlorinated methane or ethane. We have also found that there are differences in the association of eX- cessive chlorine atoms in the last mentioned group of low molecular weight to short chain halogenated compounds as compared with the instability of chlorinated high molecular weight paraflinic derivatives mentioned earlier.

Now we have discovered a highly satisfactory stabilization of aliphatic and in particular of ethylenic halogenated hydrocarbons having one or two carbon atoms and from two to four chlorine atoms per molecule, such as trichloroethylene, perchloroethylene, tetrachloroethane and trichloroethanes which can be attained as set forth as the objects of our invention, under avoidance of the drawbacks of the known methods, by treating the hydrocarbon to be stabilized with a stabilizing agent which is an inorganic sulfur compound having only one sulfur atom per molecule which sulfur atom is bonded oxidically and tetravalently, preferably to oxygen alone. In the latter case, the stabilizing agent used is gaseous sulfur dioxide. Surprisingly enough, and contrary to a belief predominant in the art, we have discovered that sulfur dioxide is a very satisfactory stabilizing agent for the specific class of halogenated hydrocarbons described.

It is particularly advantageous that the hydrocarbon such as trichloroethylene stabilized with S0 according to the invention is free from undesirable byproducts, so that a further complicated and costly treatment for the removal of byproducts is made superfluous.

While we prefer to apply the sulfur dioxide in its gaseous form, it is also possible to add to the hydrocarbon to be stabilized such salts of sulfurous acid (H QSO as easily give off S0 Among such salts, there are the alkali metal bisulfites, in particular sodium and potassium bisulfites, and commercially easily available alkali earth metal bisulfites, in particular calcium bisulfite.

The stabilizing effect of sulfur dioxide can be further enhanced by using the same in combination with certain known stabilizing agents with which the hydrocarbon to be stabilized is treated either prior to, simultaneous with, or after the treatment with S0 These auxiliary stabilizers are used in very small amounts, such as about 0.01 to 0.05% of the hydrocarbon to be stabilized, while the amounts of S0 required simultaneously or preferably prior to the application of the auxiliary stabilizer, are larger, in the order 3 of from 0.03 to 3% by weight of the instable hydrocarbon.

As auxiliary stabilizers we use certain organic reducing agents, which are ethylenic or acetylenic hydrocarbons having at least three or four or even a greater number of double or triple bonds per molecule. Thus, butenes, pentenes, Z-methyl-pentene-l, hexenes, tcrpencs and, with especially favorable results, myrcene which contains eight carbon atoms per molecule, and above all, isoprene, have been used by us.

Another group also used by us successfully as auxiliary stabilizing agents in addition to sulfur dioxide is constituted by the cyclenes such as cyclopentene, cyclohexene, cyclooctatetrene and the like.

It is also possible to use certain reducing agents such as aliphatic aldehydes or ketones which form association compounds with S and sulfites, bisulfites and hydrosulfites, for instance the formaldehyde hydrosulfite complex and similar compounds.

Other auxiliary stabilizers that can be used in small amounts to enhance further the stabilizing effect of S0 or eventually the sulfites, bisulfites and hydrosulfites mentioned above, are certain nitrogenated reducing compounds such as nitrites, guanidines, diazonium compounds, or derivatives of the organic compounds which may contain in their molecules other elements such as halogens, phosphorus or metals.

While treatments with the above-listed stabilizers alone have proved in the past to be too complicated and/or costly, and often of unsatisfactory result, the treatment With S0 by the method according to our invention permits to attain a high degree of stability with a cheap, easily available agent that can be handled easily and leaves no undesirable byproducts in the stabilized halogenated hydrocarbon. The auxiliary stabilizers to be used to further augment the stability of the hydrocarbon, While more costly, can be applied in much smaller quantity, and are chosen from among those of the known stabilizers which are least inclined to leave undesirable byproducts in the stabilized end product.

The treatment with gaseous sulfur dioxide according to the invention is best eifected by Working under a pressure higher than atmospheric, for instance at temperatures between 0 and 80 C. under pressures above 1 up to 5 atmospheres.

The treatment with 80;; and an auxiliary stabilizer may be carried out in practice, for instance, by first introducing the auxiliary stabilizer, in particular an organic reducing agent, into the instable hydrocarbon and then to cause S0 to be absorbed in the hydrocarbon under pressure.

A, recommendable mode of operation comprises the steps of first stabilizing the instable hydrocarbon with S0 gas thereby permitting transportation of the hydrocarbon in storage tanks, and then adding at a location of use, further auxiliary stabilizers to the hydrocarbon prestabilized with S0 The secondary stabilization is made much more effective by the fact that the hydrocarbon has been pre-treated with sulfur dioxide.

According to another mode of operation, the treatment is carried out with S0 or similar stabilizers containing tetravalent sulfur bonded to oxygen atoms in their molecules, in mixture with known auxiliary stabilizers.

It is desirable that the hydrocarbons stabilized according to the invention leave substantially no residues when distilled. Therefore, both those sulfurous and those auxiliary stabilizers are preferred which are volatilizible and can be easily entrained by the stabilized hydrocarbon during the distillation of the latter.

Excellent results are, for instance achieved, if an instable hydrocarbon is first stabilized with sulfur dioxide gas and then with an addition of morpholine.

The effect of the treatment with tetravalent sulfur compounds according to the invention can be illustrated by tests carried out with trichloroethylene, after 48 hours of oxidation in an oxygen current, and catalyzed by illumination with white light. A trichloroethylene stabilized conventionally with pyridine and triethylamine yields in the above oxidation tests an acidity content of 0.13%, calculated as HCl, the same trichloroethylene pretreated with S0 gas according to the invention, with 0.03% by weight of S0 and then further stabilized with pyridine and trialkylamine, shows an acidity of less than half the above value.

Similarly, a trichloroethylene stabilized in a conventional manner with a mixture of triethylamine and thymol, shows, after the above-mentioned oxidation test, an acidity of 0.5% by weight (HCl); after treating the same instable trichloroethylene first with $0 and then with isoprene as an auxiliary stabilizer, shows an acidity of only 0.04%, after the same test. Trichloroethylene pretreated with S0 and then with pyridine as an auxiliary stabilizer shows an acidity of only 0.007%.

The invention shall be further illustrated by a number of examples which are, however, not to be considered limitative in any way of the scope of the invention.

Example I 140 kg. (kilograms) of perchloroethylene are stirred during 5 hours at room temperature and at a speed of rpm. in 20 liters of an aqueous solution containing 2 kg. of sodium bisulfite dissolved therein. The perchloroethylene is then decanted, washed several times with Water, then distilled at to 122 C., and pyridine at a rate of 0.01% by weight is added to the distillate.

A corrosion test on an iron surface which is in contact during 3 hours in the dark with the .boiling stabilized distillate, shows that the latter does not attack the iron in any Way, neither in the vapor nor in the liquid phase.

A comparative test, carried out under similiar conditions with a trichloroethylene stabilized with pyridine alone shows a clear attack of the iron surface by the trichloroethylene vapors.

Example II The stabilization of trichloroethylene is carried out in a container provided with a stirring mechanism and a reflux condenser, as well as a tube opening near the bottom of the container. The apparatus is charged with 100 kg. of trichloroethylene to which 50 grams of hydroquinone are added. On the other hand, a current of sulfur dioxide gas is caused to bubble through isoprene in a cooled flask under a temperature maintained between 0 and 5 C., from which flask the sulfur dioxide laden with isoprene vapors is directed through the aforesaid tube below the surface of the trichloroethylene in the container and caused to bubble through the latter, while the trichloroethylene is vigorously stirred, for instance, at 200 rpm. In the course of 3 hours, the sulfur dioxide stream transports about 1500 grams of isoprene into the trichloroethylene, while the temperature of the latter rises gradually from room temperature to about 70 C. At the same time, the trichloroethylene in the container absorbs about 2500 grams of sulfur dioxide. The stream of the latter is then interrupted and the excess of S0 expelled from the container by a. stream of nitrogen passed through the tube dipping into the trichloroethylene.

The pre-stabilized trichloroethylene is then filtered to eliminate any excessive hydroquinone Which had been added initially to prevent any polymerisation of the introduced isoprene.

The stability of the end product is very satisfactory, but may be further enhanced by adding auxiliary stabilizers, for instance triethylamine and thymol or pyridine, whereby the trichloroethylene becomes virtually inert to the action of metals even in the heat.

Example III 1000 kg. of trichloroethylene are stirred during three Example IV Example IH is repeated, but to 1000 kg. of SO -pretreated trichloroethylene, there are added 275 grams of morpholine, instead of pyridine and triethylamine. Oxidation tests show a residual acidity of only 0.02%. Distillation of the stabilized end product leaves no residue.

Example V 1000 grams of trichloroethylene are stirred together with 400 milligrams of cyclohexene and 150 milligrams of triethylamine at a speed of 150 rpm. during three hours while S gas is intnoduced, maintaining an S0; pressure between 3 and 6 kg./cm. above the hydrocarbon. The excess of S0 is then expelled and an auxiliary stabilizer of pyridine and triethylamine in amounts of 230 mg. and 20 mg. respectively is added to the product. The acidity value attained after oxidation tests is below 0.01% (I-ICl).

Example VI 1000 grams of trichloroethylene stabilized, as described in the preceding example, with 400 mg. of cyclohexene, pyridine and triethylamine, but without pre-treatment with SO are subjected to the same oxidation tests and show an acidity value in the order of 0.07% (HCl).

We believe that the unexpected prestabilizing efiect of tetravalent, oxidically bonded sulfur in S0 and similar compounds discovered by us, is due to the addition of sulfonic substituent groups at the double linkages or triple linkages in the trichloroethylene and the like molecule, at the same time expelling loosely covalently bonded cblorine atoms from the molecule.

At the same time, there is no danger that the formation of the corresponding sulfonic additive compounds is accompanied by any disturbing formation of colloidal sulfur, or of undesirable poisonous or malodorous compounds.

The fact that the pre-s-tabilizing agent containing a tetravalent, oxidically bonded sulfur atom per molecule, and in particular sulfur dioxide is commercially available in large quantities and at low cost makes the method according to the invention particularly applicable on an industrial scale.

It will be understood that this invention is susceptible to further modification and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

What is claimed is:

1. A process for stabilizing halogenated aliphatic hydrocarbons selected from the group consisting of u'ichloroethylene and perchloroethylene comprising the steps of treating a hydrocarbon of the aforesaid kind with about 0.03-3% by weight of said hydrocarbon of gaseous sulfur dioxide as a stabilizing agent and with at least one reducing hydrocarbon compound selected from the group con sisting of cyclohexene and isoprene.

2. In a process for stabilizing halogenated aliphatic hydrocarbons selected from the group consisting of trichlo roethylene and perchloroethylene the step of treating the aforesaid hydrocarbon with about 0.034% by weight of said hydrocarbon of gaseous sulfur dioxide.

3. In a process for stabilizing halogenated aliphatic hydrocarbons selected from the group consisting of trichloroethylene and perchloroethylene, the steps, in com 6 bination, of iitraining isoprene in a stream of gaseous sulfur dioxide and passing such an amount of said stream laden with isoprene through said hydrocarbon that about 0.034% of sulfur dioxide by weight of said hydrocarbon is dissolved in said hydrocarbon.

4. In a process for stabilizing halogenated aliphatic hydrocarbons selected from the group consisting of triehloroethylene and perchloroethylene, the steps, in combination, of entraining isoprene in a stream of gaseous sulfur dioxide, passing said stream laden with isoprene through said hydrocarbon and expelling excessive sulfur dioxide from said hydrocarbon by passing a stream of nitrogen therethrough until there remains about 0.0-33% of sulfur dioxide by weight of said hydrocarbon.

5. In a process for stabilizing halogenated aliphatic hydrocarbons selected from the group consisting of trichloroethylene and perchloroethylene, the steps, in combination, of entraining isoprene in a stream of gaseous sulfur dioxide and passing said stream laden with isoprene through said hydrocarbon under a pressure above 1 and up to 5 atmospheres and a working temperature of 0 and C., so that about 0.033% of sulfur dioxide by weight of said hydrocarbon is dissolved in said hydrocarbon.

6. A solvent having a halogenated aliphatic hydrocarbon selected from the group consisting of trichloroethylene and perchloroethylene containing about 0.033% by weight of said hydrocarbon, a substance having tetravalent exclusively oxidically bonded sulfur atoms linked to at least part of the molecules of said hydrocarbon, and having, after artificial oxidation in an oxygen stream during 48 hours and under heating to boiling temperature in contact with a surface of iron metal an acidity calculated as HCl of less than 0.04% by weight.

7. A solvent constituted by a halogenated aliphatic hydrocarbon selected from the group consisting of trichloroethylene and perchloroethylene containing about 0.03-3% by weight of said hydrocarbon of sulfur dioxide monded to at least part of the molecule of said hydrocarbon and further containing an auxiliary stabilizing agent selected from the group consisting of isoprene, cyclohexene and pyridine and of such volatility that said hydrocarbon is distillable substantially free from leaving a residue.

8. In a process for stabilizing halogenated aliphatic hydrocarbons selected from the group consisting of trichloroethylene and perchloroethylene the step of treating the aforesaid hydrocarbon with about 0.03-3 by weight of said hydrocarbon of a stabilizing agent containing per molecule 1 tetravalent exclusively oxidically bonded sulfur atom.

9. A stabilized trichloroethylene solvent having a halogenated aliphatic hydrocarbon selected from the group consisting of trichloroethylene and perchloroethylene containing about 0.033% by weight of said hydrocarbon of a substance having tetravalent exclusively oxidically bonded sulfur atoms linked to at least part of the molecules of said hydrocarbon, and having, after artificial oxidation in an oxygen stream during 48 hours and under heating to boiling temperature in contact with a surface of iron metal an acidity calculated as HCl of less than 0.04% by weight.

10. A stabilized perchloroethylene solvent having a halogenated aliphatic hydrocarbon selected from the group consisting of trichloroethylene and perchloroethylene containing about 0.033% by weight of said hydrocarbon of a substance having tetravalent exclusively oxidically bonded sulfur atoms linked to at least part of the molecules of said hydrocarbon, and having, after artificial oxidation in an oxygen stream during 48 hours and under heating to boiling temperatures in contact with a surface of iron metal an acidity calculated as HCl of less than 0.04% by weight.

11. A stabilized tetrachloroethane solvent containing a halogenated aliphatic hydrocarbon selected from the group consisting of trichloroethylene and perchloroethylene containing'about 0.033% 'by weight of said hydrocarbon of a substance having tetravalent exclusively oxidically bonded sulfur atoms linked to at least part of the molecules of said hydrocarbon, and having, after artificial oxidation in an oxygen stream during 48 hours and under heating to boiling temperature in contact With a surface of iron metal an acidity calculated as HCl of less than 0.04% by weight.

12. A stabilized trichloroethylene solvent having a halogenated aliphatic hydrocarbon selected from the group consisting of trichloroethylene and perchloroethylene containing about 0.033% by Weight of said hydrocarbon of a substance having tetravalent exclusively oxidically bonded sulfur atoms linked to at least part of the molecules of said hydrocarbon, and from about 0.01 to 0.05% by weight of isoprene, and having, after artificial oxidation in an oxygen stream during 48 hours and under heating to boiling temperatures in contact with a surface of iron metal an acidity calculated as HCl of less than 0.04% by Weight.

13. A stabilized trichloroethylene solvent having a halogenated aliphatic hydrocarbon selected from the group consisting of trichloroethylene and perchloroethylene containing about 0.03-3% by weight of said hydrocarbon of a substance having tetravalent exclusively oxidically bonded sulfur atoms linked to at least part of the molecules of said hydrocarbon, and from about 0.01 to 0.05% by weight of isoprene, pyridine, and triethylamine, and having, after artificial oxidation in an oxygen stream during 48 hours and under heating to boiling temperatures in contact With a surface of iron metal an acidity calculated as HCl of less than 0.04% by weight.

8 14; A stabilized trichloroethylene containing about 0.033% by weight of said hydrocarbon of a substance having tetravalent exclusively oxidically bonded sulfur atoms, and about 0.0 1 to 0.05% of cyclohexene, triethylamine and pyridine, and having, after artificial oxidation in an oxygen stream during 48 hours and under heating to boiling temperature in contact with a surface of iron metal an acidity calculated as HCl of less than 0.04% by weight.

15. A stabilized trichloroethylene containing about 0.033% by weight of said hydrocarbon of a substance having tetravalent exclusively oxidically bonded sulfur atoms and about 0.01 to 0.05 of morpholine, and having after artificial oxidation in anoxygen stream during 48 hours and under heating to boiling temperature in contact with a surface of iron metal an aciditycalculated as HCl of less than 0.04% by Weight.

References Cited in the file of this patent (1st addition to No. 649,934, Sept. 10, 

1. A PROCESS FOR STABILIZING HALOGENATED ALIPHATIC HYDROCARBONS SELECTED FROM THE GROUP CONSISTING OF TRICHLOROETHYLENE AND PERCHOROETHLENE COMPRISING THE STEPS OF TREATING A HYDROCARBON OF THE AFORESAID KIND WITH ABOUT 0.03-3% BY WEIGHT OF SAID HYDROCARBON OF GASEOUS SULFUR DIOXIDE AS A STABILIZING COMPOUND SELECTED FROM THE GROUP CONING HYDROCARBON COMPOUND SELECTED FROM THE GROUP CONSISTING OF CYCLOHEXENE AND ISOPRENE. 